The U.S. prison population is aging; increasing numbers of older adults are being incarcerated and even more are aging in place. Older (age >50) inmates are the fastest growing segment of the prison population and have the system's highest suicide rates. Pilot study data from 146 older inmates in 3 Connecticut state prisons (56% White, 28% Black, 9% Hispanic, 6% Other; ages 50-83) supporting this application indicate that older inmates are likely to experience depression and suicidal ideation (SI) - each a strong predictor of suicide among those living on the inside and in the community. These data also show that conventional factors associated with increased suicide risk in mixed-age inmate samples, such as time served or single-cell housing, appear less relevant for older inmates. Instead, geriatric considerations indicating diminished physical capacity, including decreased activities of daily living (ADLs) and physical vulnerability or frailty, may assume a far greater importance in identifying older inmates at risk of depression and SI. Furthermore, prison is a unique place to age. Inmates may fear for their safety or have privileges revoked due to facility-wide lockdowns. There are also ADLs specific to prison (prison ADLs or PADLs) including climbing on/off the top bunk and walking to chow. The goal of this research, the Aging Inmates' Suicidal Ideation and Depression (Aging INSIDE) Study, is to determine how physical capacity and unique demands of the prison environment may impact older inmates' likelihood of experiencing depression and SI, focusing on two questions: Are geriatric factors that indicate diminished physical capacity useful for identifying older inmates at increased risk of experiencing depression and SI? Do environmental factors unique to prison affect change in one's physical capabilities over time, ultimately impacting older inmates' likelihood of experiencing depression and SI? Aging INSIDE will answer these questions by using a longitudinal study design and by recruiting a sample of 250 sentenced inmates age >50 from 10 Connecticut state prisons, collecting data at baseline and 12 months from complementary sources (self- and performance-based assessments, medical chart review, offender-based data). In the short term, findings from Aging INSIDE will inform risk assessment and detection of depression and SI in older inmates, a highly understudied and rapidly growing segment of inmates with high suicide rates. In the longer term, knowledge gained will help determine an optimal point of intervention (e.g., onset of PADL disability or frailty) and opportunities for prevention (e.g., accommodations for disability) of still modifiable risk factors among older inmates. By considering the influence of the unique prison environment on older inmates' individual physical capacities, Aging INSIDE pushes the state of suicide-related research in prison towards more individualized risk reduction and prevention. Finally, Aging INSIDE is also innovative as it focuses on older inmates; a vulnerable and largely understudied population concentrated in a challenging setting for conducting research. We have included an ethical consultant to ensure protection of study participants' rights.